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  <meta name="description" content="passwd​ ，  sudo​ ， ping​  等命令会修改关键文件，确保非root​ 用户无法修改，因此需要转换为root​ 用户，而setuid​ 位可以让用户暂时获得文件拥有者root​ 的身份。 以ping 命令为例，删除s 位后无法ping ，因为没有打开socket 的权限。而当将s 位重新设置时，又可以ping  ：">
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          Linux 权能机制
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        <ol>
<li><p><code>passwd​</code> ，  <code>sudo​</code> ， <code>ping​</code>  等命令会修改关键文件，确保非<code>root​</code> 用户无法修改，因此需要转换为<code>root​</code> 用户，而<code>setuid​</code> 位可以让用户暂时获得文件拥有者<code>root​</code> 的身份。</p>
<p>以<code>ping</code> 命令为例，删除<code>s</code> 位后无法<code>ping</code> ，因为没有打开<code>socket</code> 的权限。而当将<code>s</code> 位重新设置时，又可以<code>ping</code>  ：</p>
<a id="more"></a>

<p><img src="setuid-ping.png" alt="选区_047"></p>
<p>为了执行权限检查，传统的 UNIX 实现区分两种类型的进程：特权进程（其有效用户 ID 为0，称为超级用户或 root），和非特权用户（其有效 UID 非0）。特权进程绕过所有的内核权限检查，而非特权进程受基于进程的认证信息（通常是：有效 UID，有效 GID，和补充组列表）的完整权限检查的支配。</p>
<p>自内核 2.2 版本开始，Linux 将传统上与超级用户关联的特权分为几个单元，称为 capabilities （权能），它们可以被独立的启用或禁用。权能是每个线程的属性。权能相当于规范了你这个程序所拥有的权限。相当于特权的需求的细化。当执行特权操作的时候，可以查看是否有相应的权能。</p>
<p><code>ping</code> 命令需要<code>CAP_NET_RAW</code>的权能，使用<code>setcap</code>为其添加权能：</p>
<p><img src="%E9%80%89%E5%8C%BA_051.png" alt="选区_050"></p>
<p>可以<code>ping</code> ，且没有设置<code>uid</code> 位。</p>
</li>
<li><p>使用<code>man capabilities</code>  可以查看权能列表及相应的解释：</p>
</li>
</ol>
<ul>
<li><p><strong>CAP_AUDIT_CONTROL</strong>（自 Linux 2.6.11）<br>启用和禁用内核审计；修改审计过滤器规则；提取审计状态和过滤规则。</p>
</li>
<li><p><strong>CAP_AUDIT_READ</strong>（自 Linux 3.16）<br>允许通过一个多播 netlink socket 读取审计日志。</p>
</li>
<li><p><strong>CAP_AUDIT_WRITE</strong>（自 Linux 2.6.11）<br>向内核审计日志写记录。</p>
</li>
<li><p><strong>CAP_BLOCK_SUSPEND</strong>（自 Linux 3.5）<br>可以阻塞系统挂起（<strong>epoll</strong>(7) <strong>EPOLLWAKEUP</strong>，<em>/proc/sys/wake_lock</em>）的特性。</p>
</li>
<li><p><strong>CAP_CHOWN</strong><br>对文件的 UIDs 和 GIDs 做任意的修改（参考 <strong>chown</strong>(2)）。</p>
</li>
<li><p><strong>CAP_DAC_OVERRIDE</strong><br>绕过文件的读，写，和执行权限检查。（DAC 是 “discretionary access control” 的缩写。）</p>
</li>
<li><p>CAP_DAC_READ_SEARCH</p>
<ul>
<li>绕过文件的读权限检查和目录的读和执行权限检查；</li>
<li>调用 <strong>open_by_handle_at</strong>(2)。</li>
</ul>
</li>
<li><p>CAP_FOWNER</p>
<ul>
<li>对于通常要求进程的文件系统 UID 与文件的 UID 匹配的操作，绕过权限检查 (比如，<strong>chmod</strong>(2)，<strong>utime</strong>(2))，除了那些包含在 <strong>CAP_DAC_OVERRIDE</strong> 和 <strong>CAP_DAC_READ_SEARCH</strong> 中的操作；</li>
<li>为任意文件设置扩展文件属性(参考 <strong>chattr</strong>(1))；</li>
<li>为任意文件设置访问控制表(ACLs)；</li>
<li>对文件删除操作忽略目录的 sticky 位；</li>
<li>在 <strong>open</strong>(2) 和 <strong>fcntl</strong>(2) 任意文件时设置 <strong>O_NOATIME</strong>。</li>
</ul>
</li>
<li><p><strong>CAP_FSETID</strong><br>当文件修改时不清除 set-user-ID 和 set-group-ID 模式位；为文件 GID 与调用进程的文件系统或补充 GIDs 不匹配的文件设置 set-group-ID 位。</p>
</li>
<li><p><strong>CAP_IPC_LOCK</strong><br>锁定内存 (<strong>mlock</strong>(2)，<strong>mlockall</strong>(2)，<strong>mmap</strong>(2)，<strong>shmctl</strong>(2))。</p>
</li>
<li><p><strong>CAP_IPC_OWNER</strong><br>绕过对 System V IPC 对象的操作的权限检查。</p>
</li>
<li><p><strong>CAP_KILL</strong><br>绕过发送信号 (参考 <strong>kill</strong>(2)) 时的权限检查。这包括使用 <strong>ioctl</strong>(2) <strong>KDSIGACCEPT</strong> 操作。</p>
</li>
<li><p><strong>CAP_LEASE</strong>（自 Linux 2.4）<br>为任意文件建立租约 (参考 <strong>fcntl</strong>(2))。</p>
</li>
<li><p><strong>CAP_LINUX_IMMUTABLE</strong><br>设置<strong>FS_APPEND_FL</strong> 和 <strong>FS_IMMUTABLE_FL</strong> inode 标记 (参考 <strong>chattr</strong>(1))。</p>
</li>
<li><p><strong>CAP_MAC_ADMIN</strong>（自 Linux 2.6.25）<br>覆盖强制访问控制 (Mandatory Access Control (MAC)). 为 Smack Linux 安全模块(Linux Security Module (LSM)) 而实现。</p>
</li>
<li><p><strong>CAP_MAC_OVERRIDE</strong>（自 Linux 2.6.25）<br>允许 MAC 配置或状态改变。为 Smack LSM 而实现。</p>
</li>
<li><p><strong>CAP_MKNOD</strong>（自 Linux 2.4）<br>使用 <strong>mknod</strong>(2) 创建特殊文件。</p>
</li>
<li><p>CAP_NET_ADMIN</p>
<p>执行多种网络有关的操作：</p>
<ul>
<li>接口配置；</li>
<li>IP 防火墙，地址伪装，和账单管理；</li>
<li>修改路由表；</li>
<li>为透明代理绑定任何地址；</li>
<li>设置服务类性 (type-of-service (TOS))；</li>
<li>清理驱动统计资料；</li>
<li>设置混杂模式；</li>
<li>启用组播；</li>
<li>使用 <strong>setsockopt</strong>(2) 设置下列 socket 选项：<strong>SO_DEBUG</strong>，<strong>SO_MARK</strong>，<strong>SO_PRIORITY</strong> (在0到6范围之外的优先级)，<strong>SO_RCVBUFFORCE</strong>，和 <strong>SO_SNDBUFFORCE</strong>。</li>
</ul>
</li>
<li><p><strong>CAP_NET_BIND_SERVICE</strong><br>将一个 socket 绑定到一个互联网域特权端口 (端口号小于 1024)。</p>
</li>
<li><p><strong>CAP_NET_BROADCAST</strong><br>(未使用) 使 socket 发送组播，并监听组播。</p>
</li>
<li><p>CAP_NET_RAW</p>
<ul>
<li>使用 RAW 和 PACKET sockets；</li>
<li>为透明代理绑定任何地址。</li>
</ul>
</li>
<li><p><strong>CAP_SETGID</strong><br>执行任意的进程 GIDs 和补充 GID 列表管理；当通过 UNIX 域 sockets 传递 socket 认证信息时伪造 GID；在一个用户命名空间 (参考 <strong>user_namespaces</strong>(7)) 中写入组 ID 映射。</p>
</li>
<li><p>CAP_SETFCAP (since Linux 2.6.24)<br>设置文件的权能。</p>
</li>
<li><p>CAP_SETPCAP</p>
<p>如果文件权能不受支持：授予或删除调用者功能设置位或来自任何其他进程的任何权能。 （当内核配置为支持文件功能时，CAP_SETPCAP的此属性不可用，因为CAP_SETPCAP对于这样的内核具有完全不同的语义。）</p>
<p>如果支持文件权能：从调用线程的边界集中添加任意权能到其可继承位;从边界集中删除权能（通过prctl（2）PR_CAPBSET_DROP）;</p>
<pre><code>对securebits标志进行更改。</code></pre></li>
<li><p>CAP_SETUID</p>
</li>
</ul>
<ul>
<li><p>CAP_SYS_ADMIN</p>
<ul>
<li>执行一系列系统管理操作，包括：<strong>quotactl</strong>(2)，<strong>mount</strong>(2)，<strong>umount</strong>(2)，<strong>swapon</strong>(2)，<strong>swapoff</strong>(2)，<strong>sethostname</strong>(2)，和 <strong>setdomainname</strong>(2)；</li>
<li>执行特权 syslog(2) 操作 (自 Linux 2.6.37 开始，应该使用 CAP_SYSLOG 来允许这一操作)；</li>
<li>执行 <strong>VM86_REQUEST_IRQ vm86</strong>(2) 命令；</li>
<li>对任意 System V IPC 对象执行 IPC_SET 和 IPC_RMID 操作；</li>
<li>覆盖 RLIMIT_NPROC 资源限制；</li>
<li>执行 trusted 和 security Extended Attributes (see <strong>xattr</strong>(7)) 操作；</li>
<li>使用 <strong>lookup_dcookie</strong>(2)；</li>
<li>使用 ioprio_set(2) 来分配 IOPRIO_CLASS_RT 和 (Linux 2.6.25 之前) IOPRIO_CLASS_IDLE I/O 调度类别；</li>
<li>当通过 UNIX 域 sockets 传递 socket 认证信息时伪装 PID；</li>
<li>在系统调用打开文件 (比如，<strong>accept</strong>(2)，<strong>execve</strong>(2)，<strong>open</strong>(2)，<strong>pipe</strong>(2)) 时，超出 /proc/sys/fs/file-max，系统范围内打开文件数的限制；</li>
<li>通过 <strong>clone</strong>(2) 和 <strong>unshare</strong>(2) 使用 <strong>CLONE_*</strong> 标记创建新的命名空间（但是，自从 Linux 3.8 开始，创建命名空间不需要任何权能）；</li>
<li>调用 <strong>perf_event_open</strong>(2)；</li>
<li>访问特权 perf 事件信息；</li>
<li>调用 <strong>setns</strong>(2) (在目标命名空间中需要 CAP_SYS_ADMIN)；</li>
<li>调用 <strong>fanotify_init</strong>(2)；</li>
<li>调用 <strong>bpf</strong>(2)；</li>
<li>执行 <strong>KEYCTL_CHOWN</strong> 和 <strong>KEYCTL_SETPERM keyctl</strong>(2) 操作；</li>
<li>执行 <strong>madvise</strong>(2) <strong>MADV_HWPOISON</strong> 操作；</li>
<li>使用 <strong>TIOCSTI ioctl</strong>(2) 向一个终端的输入队列中插入字符，而不是调用者的控制终端；</li>
<li>使用废弃的 <strong>nfsservctl</strong> (2) 系统调用；</li>
<li>使用废弃的 <strong>bdflush</strong> (2) 系统调用；</li>
<li>执行各种特权的块设备 <strong>ioctl</strong>(2) 操作；</li>
<li>执行各种特权的文件系统 <strong>ioctl</strong>(2) 操作；</li>
<li>对许多设备驱动执行管理操作。</li>
</ul>
</li>
<li><p><strong>CAP_SYS_BOOT</strong><br>使用 <strong>reboot</strong>(2) 和 <strong>kexec_load</strong>(2)。</p>
</li>
<li><p><strong>CAP_SYS_CHROOT</strong><br>使用 <strong>chroot</strong>(2)。</p>
</li>
<li><p><strong>CAP_SYS_MODULE</strong><br>加载和卸载内核模块(参考 <strong>init_module</strong>(2) 和 <strong>delete_module</strong>(2))；在 2.6.25 之前的内核中：从系统范围内的权能边界集合中丢弃权能。</p>
</li>
<li><p>CAP_SYS_NICE</p>
<ul>
<li>触发进程 nice 值 (<strong>nice</strong>(2)，<strong>setpriority</strong>(2)) 和为任意进程改变 nice 值；</li>
<li>为调用进程设置实时调度策略，及为任意进程设置调度策略和优先级 (<strong>sched_setscheduler</strong>(2)，<strong>sched_setparam</strong>(2)，<strong>shed_setattr</strong>(2))；</li>
<li>为任意进程设置 CPU affinity (<strong>sched_setaffinity</strong>(2))；</li>
<li>为任意进程设置 I/O 调度类别和优先级 (<strong>ioprio_set</strong>(2))；</li>
<li>对任意进程应用 <strong>migrate_pages</strong>(2) 并允许进程被迁移到任意节点；</li>
<li>对任意进程应用 <strong>move_pages</strong>(2)；</li>
<li>在 <strong>mbind</strong>(2) 和 <strong>move_pages</strong>(2) 中使用 <strong>MPOL_MF_MOVE_ALL</strong> 标记。</li>
</ul>
</li>
<li><p><strong>CAP_SYS_PACCT</strong><br>使用 <strong>acct</strong>(2)。</p>
</li>
<li><p>CAP_SYS_PTRACE</p>
<ul>
<li>使用 <strong>ptrace</strong>(2) 追踪任意进程；</li>
<li>对任意进程应用 <strong>get_robust_list</strong>(2)；</li>
<li>使用 <strong>process_vm_readv</strong>(2) 和 <strong>process_vm_writev</strong>(2) 同任意进程的内存传输数据；</li>
<li>使用 <strong>kcmp</strong>(2) 检查进程。</li>
</ul>
</li>
<li><p>CAP_SYS_RAWIO</p>
<ul>
<li>执行 I/O 端口操作 (<strong>iopl</strong>(2) 和 <strong>ioperm</strong>(2))；</li>
<li>访问 /proc/kcore；</li>
<li>使用 <strong>FIBMAP ioctl</strong>(2) 操作；</li>
<li>打开设备访问 x86 模式特有寄存器 (MSRs，参考 <strong>msr</strong>(4))；</li>
<li>更新 /proc/sys/vm/mmap_min_addr；</li>
<li>在地址低于 /proc/sys/vm/mmap_min_addr 的位置创建内存映射；</li>
<li>在 /proc/bus/pci 中映射文件；</li>
<li>打开 /dev/mem 和 /dev/kmem；</li>
<li>执行各种 SCSI 设备命令；</li>
<li>在 <strong>hpsa</strong>(4) 和 <strong>cciss</strong>(4) 设备上执行某一操作；</li>
<li>在其它设备上执行一系列设备特有操作。</li>
</ul>
</li>
<li><p>CAP_SYS_RESOURCE</p>
<ul>
<li>使用 ext2 文件系统上的预留空间；</li>
<li>执行 ioctl(2) 调用控制 ext3 日志；</li>
<li>覆盖磁盘配额限制；</li>
<li>增加资源限制 (参考 <strong>setrlimit</strong>(2))；</li>
<li>覆盖 RLIMIT_NPROC 资源限制；</li>
<li>在终端分配上覆盖最大的终端数；</li>
<li>覆盖最大的 keymaps 个数；</li>
<li>允许实时时钟中断大于64 hz；</li>
<li>触发一个 System V 消息队列的 msg_qbytes 限制超过 /proc/sys/kernel/msgmnb 中的限制 (参考 <strong>msgop</strong>(2) 和 <strong>msgctl</strong>(2))；</li>
<li>当使用 <strong>F_SETPIPE_SZ fcntl</strong>(2) 命令设置一个管道的容量时覆盖 /proc/sys/fs/pipe-size-max 的限制；</li>
<li>使用 <strong>F_SETPIPE_SZ</strong> 增加管道的容量超出 /proc/sys/fs/pipe-max-size 指定的限制；</li>
<li>当创建 POSIX 消息队列 (参考 <strong>mq_overview</strong>(7)) 时覆盖 /proc/sys/fs/mqueue/queues_max 的限制；</li>
<li>使用 <strong>prctl</strong>(2) <strong>PR_SET_MM</strong> 操作；</li>
<li>设置 /proc/PID/oom_score_adj 为一个小于由一个具有 CAP_SYS_RESOURCE 的进程最近设置的值的值。</li>
</ul>
</li>
<li><p><strong>CAP_SYS_TIME</strong><br>设置系统时钟 (<strong>settimeofday</strong>(2)，<strong>stime</strong>(2)，<strong>adjtimex</strong>(2))；设置实时 (硬件) 时钟。</p>
</li>
<li><p><strong>CAP_SYS_TTY_CONFIG</strong><br>使用 <strong>vhangup</strong>(2)；对虚拟终端使用各种特权 <strong>ioctl</strong>(2) 操作。</p>
</li>
<li><p>CAP_SYSLOG</p>
<p>(自 Linux 2.6.37)</p>
<ul>
<li>执行特权 <strong>syslog</strong>(2) 操作。参考 <strong>syslog</strong>(2) 来获取哪些操作需要特权的信息；</li>
<li>当 /proc/sys/kernel/kptr_restrict 值为 1 时，查看通过 /proc 和其它接口暴露<br>的内核地址。(参考 <strong>proc</strong>(5) 中 kptr_restrict 的讨论。)</li>
</ul>
</li>
<li><p><strong>CAP_WAKE_ALARM</strong> (自 Linux 3.0)<br>触发将唤醒系统的东西 (设置 CLOCK_REALTIME_ALARM 和 CLOCK_BOOTTIME_ALARM 定时器)</p>
</li>
</ul>
<ol>
<li>找出所有设置<code>uid</code> 位程序，使用以下命令：</li>
</ol>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">find &#x2F; -perm &#x2F;u&#x3D;s</span><br><span class="line">find &#x2F; -perm -4000</span><br></pre></td></tr></table></figure>

<p>结果如下：</p>
<p><img src="%E9%80%89%E5%8C%BA_048.png" alt="选区_048"></p>
<p><img src="%E9%80%89%E5%8C%BA_049.png" alt="选区_049"></p>
<p>部分需要的权能如下：</p>
<table>
<thead>
<tr>
<th>程序</th>
<th>需要的权能</th>
</tr>
</thead>
<tbody><tr>
<td>/bin/ping</td>
<td>CAP_NET_RAW</td>
</tr>
<tr>
<td>/bin/mount</td>
<td>CAP_SYS_ADMIN</td>
</tr>
<tr>
<td>/bin/su</td>
<td>CAP_DAC_OVERRIDE,CAP_SETGID,CAP_SETUID</td>
</tr>
<tr>
<td>/bin/fusermount</td>
<td>CAP_SYS_ADMIN</td>
</tr>
<tr>
<td>/bin/umount</td>
<td>CAP_SYS_ADMIN</td>
</tr>
<tr>
<td>/usr/bin/passwd</td>
<td>CAP_CHOWN ,CAP_DAC_OVERRIDE ,CAP_FOWNER</td>
</tr>
</tbody></table>
<ol>
<li><p>在linux中，文件权能有如下三种：</p>
<ul>
<li>effective：当前有效的权能，执行某特权操作时，操作系统检查cap_effective的对应位是否有效,而不再是检查进程的有效UID是否为0。</li>
<li>permitted：当前进程所有能使用的能力，effective包含于permitted</li>
<li>inheritable：可以被继承的能力</li>
</ul>
<p>linux程序调用子程序，权能变换公式如下：</p>
<figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">P’(ambient) = (file is privileged) ? 0 : P(ambient)</span><br><span class="line">P<span class="string">'(permitted) = (P(inheritable) &amp; F(inheritable)) | (F(permitted) &amp; cap_bset)| P’(ambient)</span></span><br><span class="line">P'(effective) = F(effective) ? P'(permitted) : P’(ambient)</span><br><span class="line">P<span class="string">'(inheritable) = P(inheritable) [i.e., unchanged]</span></span><br></pre></td></tr></table></figure>

<p>其中：</p>
<ul>
<li>P denotes the value of a thread capability set before the execve(2)</li>
<li>P’ denotes the value of a capability set after the execve(2)</li>
<li>F denotes a file capability set</li>
<li>cap_bset is the value of the capability bounding set (described below).</li>
</ul>
<p>A privileged file is one that has capabilities or has the set-user-ID or set-group-ID bit set.</p>
</li>
</ol>
<p>实现一个程序其满足以下的功能：</p>
<ul>
<li>能够永久的删除其子进程的某个权能。</li>
<li>能暂时性的删除其子进程的某个权能。</li>
<li>能让上面被暂时性删除的权能重新获得</li>
</ul>
<p>以ping为例，我们知道ping需要的权能为cap_net_raw，为了能在execve后执行ping，即execve中的ping有cap_net_raw权能，根据上面的变换规则：</p>
<ul>
<li>设置/bin/ping权能为cap_net_raw+ei，使得可以继承<ul>
<li>sudo setcap cap_net_raw+ei /bin/ping</li>
</ul>
</li>
<li>设置当前的进程的权能有cap_net_raw+i权能</li>
</ul>
<p>永久删除子进程的权能就移除effective和inheritable、permitted的，暂时性删除就移除effective和inheritable的，恢复暂时性删除的就添加进effective和inheritable。</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br><span class="line">87</span><br><span class="line">88</span><br><span class="line">89</span><br><span class="line">90</span><br><span class="line">91</span><br><span class="line">92</span><br><span class="line">93</span><br><span class="line">94</span><br><span class="line">95</span><br><span class="line">96</span><br><span class="line">97</span><br><span class="line">98</span><br><span class="line">99</span><br><span class="line">100</span><br><span class="line">101</span><br><span class="line">102</span><br><span class="line">103</span><br><span class="line">104</span><br><span class="line">105</span><br><span class="line">106</span><br><span class="line">107</span><br><span class="line">108</span><br><span class="line">109</span><br><span class="line">110</span><br><span class="line">111</span><br><span class="line">112</span><br><span class="line">113</span><br><span class="line">114</span><br><span class="line">115</span><br><span class="line">116</span><br><span class="line">117</span><br><span class="line">118</span><br><span class="line">119</span><br><span class="line">120</span><br><span class="line">121</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;stdio.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;stdlib.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;string.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;sys/types.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;unistd.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;sys/capability.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;sys/prctl.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">undef</span> _POSIX_SOURCE</span></span><br><span class="line"></span><br><span class="line"><span class="keyword">extern</span> <span class="keyword">int</span> errno;</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">void</span> <span class="title">whoami</span><span class="params">()</span> </span>&#123;</span><br><span class="line">    <span class="built_in">printf</span>(<span class="string">"uid=%i  euid=%i  gid=%i\n"</span>, getuid(), geteuid(), getgid());</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">void</span> <span class="title">listCaps</span><span class="params">()</span></span>&#123;</span><br><span class="line">    <span class="keyword">cap_t</span> caps = cap_get_proc();</span><br><span class="line">    <span class="keyword">ssize_t</span> y = <span class="number">0</span>;</span><br><span class="line">    <span class="built_in">printf</span>(<span class="string">"The Process %d was give capabilities %s\n"</span>,(<span class="keyword">int</span>) getpid(), cap_to_text(caps, &amp;y));</span><br><span class="line">    fflush(<span class="number">0</span>);</span><br><span class="line">    cap_free(caps);</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">void</span> <span class="title">do_ping</span><span class="params">()</span></span>&#123;</span><br><span class="line">	<span class="keyword">if</span>(!fork())&#123;</span><br><span class="line">		whoami();</span><br><span class="line">		listCaps();</span><br><span class="line">		execlp(<span class="string">"ping"</span>,<span class="string">"ping"</span>,<span class="string">"-c 1"</span>,<span class="string">"localhost"</span>,<span class="literal">NULL</span>);</span><br><span class="line">	&#125;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">void</span> <span class="title">init</span><span class="params">()</span></span>&#123;</span><br><span class="line">	<span class="keyword">if</span>(getuid() != <span class="number">0</span>)&#123;</span><br><span class="line">		<span class="built_in">puts</span>(<span class="string">"请使用sudo执行本程序"</span>);</span><br><span class="line">		<span class="built_in">exit</span>(<span class="number">1</span>);</span><br><span class="line">	&#125;</span><br><span class="line">		</span><br><span class="line">	<span class="keyword">cap_value_t</span> cap_values[] = &#123;CAP_SETUID, CAP_SETGID, CAP_SETPCAP ,CAP_NET_RAW&#125;;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">cap_t</span> caps = cap_init();</span><br><span class="line">    cap_set_flag(caps, CAP_PERMITTED, <span class="number">4</span>, cap_values, CAP_SET);</span><br><span class="line">	cap_set_flag(caps, CAP_EFFECTIVE, <span class="number">4</span>, cap_values, CAP_SET);</span><br><span class="line">    cap_set_proc(caps);</span><br><span class="line">    prctl(PR_SET_KEEPCAPS, <span class="number">1</span>, <span class="number">0</span>, <span class="number">0</span>, <span class="number">0</span>);</span><br><span class="line">    cap_free(caps);</span><br><span class="line"></span><br><span class="line">    setgid(<span class="number">1000</span>);</span><br><span class="line">	setuid(<span class="number">1000</span>);</span><br><span class="line">	</span><br><span class="line">    caps = cap_get_proc();</span><br><span class="line">    cap_set_flag(caps, CAP_EFFECTIVE, <span class="number">4</span>, cap_values, CAP_SET);</span><br><span class="line">	cap_set_flag(caps, CAP_INHERITABLE, <span class="number">4</span>, cap_values, CAP_SET);</span><br><span class="line">    cap_set_proc(caps);</span><br><span class="line">    cap_free(caps);</span><br><span class="line">	whoami();</span><br><span class="line">	listCaps();</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">void</span> <span class="title">printInfo</span><span class="params">()</span></span>&#123;</span><br><span class="line">	<span class="built_in">puts</span>(<span class="string">"\n------权能测试小程序------\n\</span></span><br><span class="line"><span class="string">请输入如下字符:\n\</span></span><br><span class="line"><span class="string">1 : 永久的删除其子进程的某个权能\n\</span></span><br><span class="line"><span class="string">2 : 暂时性的删除其子进程的某个权能\n\</span></span><br><span class="line"><span class="string">3 : 暂时性删除的权能重新获得\n\</span></span><br><span class="line"><span class="string">4 : ping -c 1 localhost\n\</span></span><br><span class="line"><span class="string">5 : 查看当前权能\n\</span></span><br><span class="line"><span class="string">q : 退出\n\</span></span><br><span class="line"><span class="string">---------------------------\n"</span>);</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">(<span class="keyword">int</span> argc, <span class="keyword">char</span> **argv)</span></span></span><br><span class="line"><span class="function"></span>&#123;</span><br><span class="line">	init();</span><br><span class="line">	<span class="keyword">char</span> <span class="built_in">line</span>[<span class="number">128</span>];</span><br><span class="line">	printInfo();</span><br><span class="line">	<span class="keyword">while</span>(fgets(<span class="built_in">line</span>, <span class="keyword">sizeof</span>(<span class="built_in">line</span>), <span class="built_in">stdin</span>))&#123;</span><br><span class="line">		<span class="keyword">char</span> cmd = <span class="built_in">line</span>[<span class="number">0</span>];</span><br><span class="line"></span><br><span class="line">		<span class="keyword">if</span>(cmd == <span class="string">'1'</span> || cmd == <span class="string">'2'</span> || cmd == <span class="string">'3'</span>)&#123;</span><br><span class="line">			<span class="built_in">printf</span>(<span class="string">"输入要操作的权能名，如cap_net_raw\n"</span>);</span><br><span class="line">			fgets(<span class="built_in">line</span>, <span class="keyword">sizeof</span>(<span class="built_in">line</span>), <span class="built_in">stdin</span>);</span><br><span class="line">			<span class="built_in">line</span>[<span class="built_in">strlen</span>(<span class="built_in">line</span>) - <span class="number">1</span>] = <span class="string">'\0'</span>;</span><br><span class="line">			<span class="keyword">cap_value_t</span> temp;</span><br><span class="line">			<span class="keyword">if</span>(cap_from_name(<span class="built_in">line</span>, &amp;temp) &lt; <span class="number">0</span>)&#123;</span><br><span class="line">				<span class="built_in">printf</span>(<span class="string">"Error capability name\n"</span>);</span><br><span class="line">			&#125;</span><br><span class="line">			<span class="keyword">else</span>&#123;</span><br><span class="line">				<span class="keyword">cap_t</span> caps = cap_get_proc();</span><br><span class="line"></span><br><span class="line">				<span class="keyword">if</span>(cmd == <span class="string">'3'</span>)&#123;</span><br><span class="line">					cap_set_flag(caps, CAP_EFFECTIVE, <span class="number">1</span>, &amp;temp, CAP_SET);</span><br><span class="line">					cap_set_flag(caps, CAP_INHERITABLE, <span class="number">1</span>, &amp;temp, CAP_SET);</span><br><span class="line">				&#125;</span><br><span class="line">				<span class="keyword">else</span>&#123;</span><br><span class="line">					cap_set_flag(caps, CAP_EFFECTIVE, <span class="number">1</span>, &amp;temp, CAP_CLEAR);</span><br><span class="line">					cap_set_flag(caps, CAP_INHERITABLE, <span class="number">1</span>, &amp;temp, CAP_CLEAR);</span><br><span class="line">					<span class="keyword">if</span>(cmd == <span class="string">'1'</span>)</span><br><span class="line">						cap_set_flag(caps, CAP_PERMITTED, <span class="number">1</span>, &amp;temp, CAP_CLEAR);</span><br><span class="line">				&#125;</span><br><span class="line">				<span class="keyword">if</span>(cap_set_proc(caps))</span><br><span class="line">					perror(<span class="string">"cap_set_proc() ERROR: "</span>);</span><br><span class="line">				<span class="keyword">else</span></span><br><span class="line">					<span class="built_in">printf</span>(<span class="string">"%s %s success\n"</span>, (cmd ==<span class="string">'3'</span>? <span class="string">"recover"</span>:<span class="string">"remove"</span>),<span class="built_in">line</span>);</span><br><span class="line"></span><br><span class="line">				cap_free(caps);</span><br><span class="line">			&#125;</span><br><span class="line">		&#125;</span><br><span class="line">		<span class="keyword">else</span> <span class="keyword">if</span>(cmd == <span class="string">'4'</span>)</span><br><span class="line">			do_ping();</span><br><span class="line"> 		<span class="keyword">else</span> <span class="keyword">if</span>(cmd == <span class="string">'5'</span>)</span><br><span class="line">			listCaps();</span><br><span class="line">		<span class="keyword">else</span> <span class="keyword">if</span>(cmd == <span class="string">'q'</span>)</span><br><span class="line">			<span class="keyword">break</span>;</span><br><span class="line">       sleep(<span class="number">1</span>);  <span class="comment">//休眠1s</span></span><br><span class="line">		printInfo();</span><br><span class="line">	&#125;</span><br><span class="line">    <span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>程序测试：</p>
<p>测试环境：</p>
<p><img src="%E9%80%89%E5%8C%BA_052.png" alt="选区_052"></p>
<p>运行程序前：<code>sudo setcap cap_net_raw+eip /bin/ping</code>  保证文件有<code>eip</code> 权能</p>
<ul>
<li>sudo apt install libcap-dev</li>
</ul>
<ul>
<li>gcc cap.c -lcap -o cap</li>
<li>sudo ./cap</li>
</ul>
<p>一开始可以<code>ping</code> :</p>
<p><img src="%E9%80%89%E5%8C%BA_053.png" alt="选区_053"></p>
<p>暂时性删除权能后无法<code>ping</code> :</p>
<p><img src="%E9%80%89%E5%8C%BA_054.png" alt="选区_054"></p>
<p>恢复后可以<code>ping</code>  :</p>
<p><img src="%E9%80%89%E5%8C%BA_055.png" alt="选区_055"></p>
<p>永久删除后无法<code>ping</code> :</p>
<p><img src="%E9%80%89%E5%8C%BA_056.png" alt="选区_056"></p>
<blockquote>
<p>参考资料：</p>
<p><a href="https://www.hrwhisper.me/introduction-to-linux-capability/#comments" target="_blank" rel="noopener">Linux setuid与权能介绍</a></p>
<p><a href="https://www.wolfcstech.com/2017/07/10/linux-capabilities-overview/" target="_blank" rel="noopener">Linux 权能综述</a></p>
</blockquote>

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